The present invention relates generally to multifiber ferrules and, more particularly, to the alignment holes, such as the guide pin holes and the alignment grooves, defined by multifiber ferrules that cooperate with alignment members to appropriately align the multifiber ferrules.
As a result of the ever increasing utilization of optical communications for both voice and data applications, multifiber connectors are being more frequently utilized in order to simultaneously interconnect a plurality of optical fibers. Not only are multifiber connectors being utilized in larger numbers, but increased performance demands are being placed upon multifiber connectors, as well as all other portions of the optical network. For example, in order to maximize signal transmission between pairs of optical fibers, multifiber connectors are required to align each of the optical fibers very precisely, especially for single mode applications. In this regard, multifiber connectors are typically required to align each optical fiber to within 7 to 14 microns for multimode applications and to within 0 to 3 microns for single mode applications.
In order to provide the desired alignment, conventional multifiber connectors include multifiber ferrules that at least partially define a pair of elongate alignment holes that receive and cooperate with respective alignment members, such as guide pins or alignment ribs, in order to appropriately align the multifiber ferrule and, in turn, the optical fibers upon which the multifiber ferrule is mounted. For example, one conventional type of multifiber ferrule is the MT ferrule, such as described by U.S. Pat. No. 5,214,730 to Sinji Nagasawa, et al., and assigned to Nippon Telephone and Telegraph Corporation of Tokyo, Japan. The MT ferrule has a generally rectangular shape in lateral cross-section and defines a pair of guide pin holes opening through the front face for receiving respective guide pins. As such, a pair of multifiber connectors having respective MT ferrules that are to be interconnected are typically configured such that one of the multifiber connectors has a male configuration and the other multifiber connector has a female configuration. The male configuration of the multifiber connector includes a pair of guide pins that have been inserted within the guide pin holes defined by the respective MT ferrule and that extend beyond the front face of the multifiber ferrule. In contrast, the female configuration of the multifiber connector includes a female MT ferrule that defines a pair of guide pin holes for receiving those portions of the guide pins that extend beyond the front face of the MT ferrule of the male connector. During mating, the insertion of the guide pins into the guide pin holes defined by the MT ferrule of the female connector aligns the connectors and, in turn, aligns the optical fibers upon which the MT ferrules are mounted. In order to snugly receive the guide pins, the guide pin holes defined by a conventional MT ferrule are cylindrical in lateral cross-section so as to have the same size and shape along their entire length. By utilizing cylindrical guide pin holes, the sidewalls that form the cylindrical guide pin holes contact the guide pins along their entire length, thereby correspondingly maximizing the alignment provided by the guide pins.
Another advantageous type of multifiber ferrule is the SC-DC multifiber ferrule provided by Siecor Corporation of Hickory, N.C., the assignee of the present invention. The SC-DC ferrule has a generally circular shape in lateral cross-section and defines a pair of alignment grooves extending along opposed side surfaces. During the mating of an SC-DC ferrule with another SC-DC ferrule, the elongate grooves defined by the opposed side surfaces of the ferrule engage respective alignment ribs or pins to align the ferrules and, in turn, the optical fibers upon which the ferrules are mounted. For example, alignment ribs are generally defined by and extend inwardly from the inner sidewalls of an alignment sleeve. Upon inserting the SC-DC ferrules into the opposed ends of the aligmnent sleeve, the alignment ribs or pins engage and are slidably advanced through the grooves defined by the respective ferrules, thereby aligning the ferrules within the alignment sleeve. As described above in conjunction with the guide pin holes defined by an MT ferrule, the alignment grooves defined by the opposed side surfaces of an SC-DC ferrule typically have the same semi-circular size and shape in lateral cross-section along their entire length. As such, the sidewalls that form the alignment grooves contact the alignment ribs or pins along their entire length, thereby correspondingly maximizing the alignment afforded by the alignment grooves and the alignment ribs or pins.
While conventional multifiber ferrules, such as the MT and SC-DC ferrules described above, effectively cooperate with alignment members, such as guide pins and alignment ribs, in order to align the optical fibers upon which the ferrules are mounted, conventional alignment techniques still suffer from several limitations. For example, attempts to insert those portions of the guide pins that protrude beyond the front face of the male configuration of an MT ferrule into the guide pin holes defined by the female configuration of an MT ferrule can sometimes initially stub the ends of the guide pins against the front face of the female MT ferrule. As such, the guide pins and/or the front face of the female MT ferrule may be damaged. At the least, this pin stubbing will increase the care and, therefore, the time that must be taken by a technician during the interconnection of a pair of multifiber ferrules. In an attempt to reduce the stubbing, the leading portion of most guide pins are tapered to facilitate insertion of the guide pins into the respective guide pin holes. As a result of the relatively small size of most guide pins that typically have a diameter of 700 microns, MT ferrules may still be misaligned by more than the diameter of the guide pin as the MT ferrules are brought into contact. In these instances, the tapered leading end of the guide pin will not serve to guide the guide pin into the respective guide pin hole, but will instead stub against the front face of the female MT ferrule.
With respect to the interaction of the alignment ribs or pins of an alignment sleeve and the elongate grooves defined by the opposed side surfaces of an SC-DC ferrule, it has been found that the alignment ribs or pins are sometimes damaged as the SC-DC ferrule is inserted into the respective alignment sleeve, thereby diminishing the precision with which the alignment ribs or pins align the optical fibers upon which the SC-DC ferrule is mounted. In this regard, it is believed that the sharp edge that defines the opening of the elongate grooves through the front face of an SC-DC ferrule oftentimes gouges the alignment ribs or pins as the SC-DC ferrule is being inserted into the respective alignment sleeve since the SC-DC ferrule is oftentimes oriented in a direction that is slightly offset from the longitudinal axis of the sleeve during its insertion into the sleeve. After being gouged by the sharp edges defined by the opening of the elongate grooves through the front face of an SC-DC ferrule, the alignment ribs or pins may no longer have the desired size and shape to cooperate with the elongate grooves for precisely aligning the respective ferrules.
Additionally, the precision with which all types of multifiber ferrules can be alignment is diminished as dirt and other particulates collect in or about the alignment holes defined by the multifiber ferrule, such as the guide pin holes defined by an MT ferrule or the elongate grooves defined by an SC-DC ferrule. In this regard, dirt and other particulates are oftentimes carried by an alignment member, such as a guide pin or an alignment rib. Upon insertion of a guide pin into a guide pin hole defined by an MT ferrule, any dirt or other particulates carried by the guide pin are typically wiped from the guide pin and collect about the circumference of the guide pin hole on the front face of the MT ferrule. Likewise, the insertion of an SC-DC ferrule into an alignment sleeve and the corresponding insertion of the alignment rib into the elongate groove defined by the SC-DC ferrule will oftentimes cause the dirt or other particulates carried by the alignment rib to be wiped from the alignment rib and collect on the front face of the SC-DC ferrule proximate the groove. While the accumulation of any amount of dirt or other particulates upon the front face of the ferrule is disadvantageous, it is possible that sufficient dirt and other particulates may accumulate upon the front face of the multifiber ferrule to prevent physical contact between the front faces of a pair of multifiber ferrules following mating of the multifiber ferrules. Without achieving physical contact between the front faces of a pair of mated multifiber ferrules, the quality of the resulting optical interconnection will likely be somewhat impaired.
These and other shortcomings of conventional multifiber ferrules are addressed by the multifiber ferrule of the present invention that includes a ferrule body that defines at least one elongate hole opening through the front face of the ferrule body that, in turn, includes a lead-in portion proximate the front face for guiding the respective alignment member into the elongate hole. As such, the multifiber ferrule of the present invention significantly reduces the occurrences of pin stubbing during the alignment of MT-type ferrules. In addition, the multifiber ferrule of the present invention significantly reduces gouging or other damage incurred by an alignment rib during the insertion of an SC or DC-type ferrule into a corresponding alignment sleeve. Finally, the lead-in portion of each elongate hole defined by the multifiber ferrule of the present invention serves as a receptacle for dirt or other particulates that are transferred from the alignment member as the alignment member is inserted into the respective elongate hole. As a result, the dirt or other particulates do not collect on the front face of the multifiber ferrule such that physical contact can continue to be established between the front faces of a pair of multifiber ferrules.
Regardless of the type of multifiber ferrule, the ferrule body at least partially defines one or more elongate holes, each having a longitudinal axis extending therethrough. Each elongate hole includes the lead-in portion proximate the front face and an adjacent alignment portion. The lead-in portion expands radially outward from the longitudinal axis in a direction extending from the adjacent alignment portion to the front face of the ferrule body. As such, the opening of the lead-in portion through the front face of the ferrule body is larger in lateral cross-section than the opening of the lead-in portion into the adjacent alignment portion. The lead-in portion is therefore capable of guiding the respective alignment member into the adjacent alignment portion that, in turn, is sized to snugly receive the alignment member, thereby serving to properly align the ferrule with the alignment members.
In one advantageous embodiment, the ferrule body fully defines the elongate hole to form a guide pin hole adapted to receive a respective guide pin. As such, the multifiber ferrule of this embodiment may be an MT-type ferrule. Alternatively, the ferrule body may only partially define the hole to thereby form an elongate groove adapted to receive a respective alignment rib. As such, the multifiber ferrule of this embodiment can be an SC or DC-type ferrule having at least one and, more typically, a pair of elongate grooves extending along the opposed side surfaces thereof.
In order to guide the respective alignment member into the adjacent alignment portion, the lead-in portion preferably has a smooth wall that expands radially outward from the longitudinal axis in the direction extending from the adjacent alignment portion toward the front face of the ferrule body. In one embodiment, the lead-in portion linearly expands in a radially outward direction from the longitudinal axis. In another embodiment, the lead-in portion expands radially outward from the longitudinal axis in a nonlinear manner such that the smooth wall of the lead-in portion is curved.
In order to guide the respective alignment member into the elongate hole while at the same time snugly engaging the alignment member so as to provide sufficiently precise alignment, the lead-in portion is preferably shorter than the adjacent alignment portion, as measured along the longitudinal axis. In this regard, the ratio of the length of the alignment portion to the length of the lead-in portion is preferably at least 4:1 and, more preferably, at least 6:1. As such, once the alignment member has been inserted into the respective hole, such as a respective guide pin hole or an elongate groove, the alignment portion snugly engages the alignment member so as to align the multifiber ferrule with another multifiber ferrule.
While the length of the lead-in portion is generally much shorter than the length of the adjacent alignment portion, the lead-in portion is preferably sized such that the lead-in portion proximate the front face is at least 50% larger in lateral cross-section than the alignment portion. As such, the multifiber ferrule of the present invention significantly reduces pin stubbing since the lead-in portion of the hole defined by the ferrule body cooperates with the tapered leading end of a guide pin to significantly increase the size of the region in which a guide pin will be appropriately guided into the hole without pin stubbing. In addition, the enlarged lead-in portion reduces gouging and other damage to an alignment rib during the insertion of an SC or DC-type ferrule into a corresponding alignment sleeve. Finally, the enlarged lead-in portion serves as a receptacle for dirt or other particulates that are wiped from the alignment member as the alignment member is inserted into the hole. As such, the dirt or other particulates do not accumulate upon the front face of the ferrule body. The multifiber ferrule of the present invention can therefore make physical contact more reliably with other multifiber ferrules during the mating process.